Conventional articles of athletic footwear include two primary elements, an upper and a sole structure. The upper provides a covering for the foot which comfortably receives and securely positions the foot with respect to the sole structure. The sole structure is secured to a lower portion of the upper and is generally located between the foot and the ground. In addition to attenuating ground reaction forces (i.e., providing cushioning) during walking, running, and other ambulatory activities, the sole structure may influence foot motions (e.g., by resisting pronation), impart stability, and provide traction, for example. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a wide variety of athletic activities.
The sole structure may generally incorporate multiple layers: a sockliner, a midsole, and an outsole. The sockliner can be a thin, compressible member located within the upper and adjacent to a plantar (i.e., lower) surface of the foot to enhance footwear comfort. The midsole can be secured to a lower surface of the upper and can form a middle layer of the sole structure. Many midsole configurations are primarily formed from a resilient polymer foam material, such as polyurethane or ethylvinylacetate, which extends throughout the length and width of the footwear. The midsole may also incorporate fluid-filled chambers, plates, moderators, or other elements that further attenuate forces, influence the motions of the foot, or impart stability, for example. The outsole forms the ground-contacting element of the footwear and may be produced from a durable and wear-resistant material (e.g., rubber) that includes texturing to improve traction.
The materials of the sole structure are generally flexible materials that bend and deform when subjected to a load, such as when a wearer of the article of footwear takes a step and/or when the wearer pivots on the forefoot of the footwear. During such motions the various regions of the sole structure, such as the forefoot, midfoot or arch, and heel regions, can flex and bend. However, these various regions of the sole structure may flex or bend to different degrees, which may result from different forces applied to the various regions, varying degrees of flexibility for each region, and/or other factors.